A cyclodextrin (hereinafter referred to as "CD") is a cyclic dextrin composed of glucoses bonded to each other by an .alpha.-1,4 bond therebetween, and .alpha.-, .beta.- and .gamma.-CD each comprising 6,7 and 8 glucoses, respectively, are well known.
These CDs have cavities in the inside of the molecule and the inside of the cavities is hydrophobic. Therefore, these have an including capacity for forming inclusion (clathrate) compounds, taking various oily substances thereinto. Accordingly, utilizing the property of them, various uses of CDs for 1 stabilization of unstable substances, 2 possession of volatile substances, 3 masking of offensive odor and 4 solubilization of hardly soluble or insoluble substances are taken into consideration.
However, .alpha.-CD and .beta.-CD have a drawback that they nave a low solubility (about several % or less) at a low temperature. In order to overcome the drawback, recently, branched CDs have been developed. Branched CDs have a constitution where a glucosyl group, a maltosyl group or a maltooligosyl group is bonded to the glucose in the CD molecule via an .alpha.-1,6 bond, and they are extremely highly soluble in water and have other various characteristics, being different from non-branched CDs.
For preparing such branched CDs, some methods have heretofore been proposed. Of them, a method which is being utilized most often industrially at present is such that a branched CD is obtained from a high concentration of maltose and the CD is produced by a condensation reaction with pullulanase. In accordance with the method, a maltosyl-CD is produced at a fairly high yield but at the same time a dimaltosyl-CD having an additional maltose of one molecule is bonded to another glycosyl group of a maltosyl-CD via an .alpha.-1,6 bond is also produced. Therefore for the purpose of isolating only a maltosyl-CD from the reaction mixture, much cost and much time are disadvantageously necessary.
Taking the above-mentioned characteristics of branched CDs into consideration, the present inventors variously investigated for the purpose of efficiently producing maltosyl-CDs. As a result, they have completed a method of producing branched CDs by bonding an .alpha.-maltosyl group to the glucosyl group of an .alpha.-, .beta.- or .gamma.-CD from a branched oligosaccharide by transglycosylation of a debranching enzyme.
In addition, they further have found that an isoamylase derived from Pseudomonas amylodelamosa is used for efficiently producing a maltosyl-CD or maltotriosyl-CD having one molecule of maltosyl group or maltotriosyl group as bonded to the glucosyl group of .alpha.-, .beta.- or .gamma.-CD via .alpha.-1,6-bond therebetween by transglycosylation. On the basis of the finding, they have completed the present invention.